Introduction

Mobile mining equipment has traditionally been fueled by diesel engines. Enhanced technology and increasing diesel prices have increased the desire for electric mining equipment, which offer many features beneficial to a mining company’s bottom line.

Electric load-haul-dump (LHD) vehicles and haul trucks have both seen increased implementation in recent years and will likely continue to increase in popularity as the world moves away from fossil fuels.

Key Considerations

Required Infrastructure

Particular infrastructure is required for some electric vehicles. Battery powered equipment requires charging stations, however infrastructure required for tethered machinery can include electric substations, transformer boxes, sockets, and more. Using cable powered vehicles such as LHDs can greatly lower operational flexibility due to the range of the machine. If the LHD were to be moved to a different location, towed diesel generators must be used to relocate both the LHD and the temporary required infrastructure. For trolley assist systems, an overhead cable is required with the infrastructure cost per truck said to be about 75% of the total truck price. [1]

Productivity

Productivity between electric equipment can vary. There are obvious limitations with tethered vehicles for operational flexibility, however they do not need to be re-fuelled like diesel powered machinery. With battery powered equipment, it is unavoidable that frequent battery changes are needed, greatly hindering availability. Although diesel engines must be fueled as well, batteries used last far less than the average shift time. [1]

Ventilation

Ventilation is needed in all underground mine operations for multiple reasons such as to provide cooling underground or clear hazardous gasses. Extensive use of diesel engines can put a strain on such ventilation systems, and raising operating costs. With many diesel engines now running at more efficient levels, mines that have underground heat as a serious concern and strain on their ventilation systems will likely find electric machinery as a justifiable choice. [1]

Maintenance

Significantly less maintenance is needed for electrically powered equipment. High skilled mechanics are needed for diesel engine upkeep and maintenance. By removing the engine from the equipment, maintenance and operating costs can be lowered. [1]

Energy Consumption

Electric machinery and electric drive motors are much more energy efficient. Diesel engine energy efficiency is about 30 – 35% and can be compared to the efficiency of electric motors which are about 90% efficient [1]. It is estimated that electric trucks will only use 24% of energy per tonne hauled. Where battery powered vehicles lack is in specific energy resulting in excessive tare weight of the machines and smaller operating time between battery changes (required change time is still significantly lower than the duration of a working shift). Diesel powered specific energy is 13 kWh/kg of fuel, whereas batteries have a maximum of 250 kWh/kg for the most efficient lithium-ion batteries.

Environmental

Incomplete combustion used in diesel engines will inherently release CO2 and other greenhouse gasses (GHG), leaving an environmental footprint. Battery powered and tethered electric equipment are considered “zero-emission” vehicles. Although trolley assist powered trucks are not “zero-emission” vehicles, they generate far less GHG than fully diesel powered haul trucks. [1]

Diesel vs. Electric Summary

Equipment

LHDs

Load-haul-dump (LHD) trucks are the most common underground electric vehicles and provide two functions: they muck and load ore at draw points or in stopes of underground mines and haul it to designated dumping points, and they load haul trucks at stockpile areas [2]. Historically LHDs have been diesel-powered, however electric LHDs (eLHDs) have gained popularity in the last decade. eLHDs may be powered using three different electric options: batteries, overhead power lines, and tethered trailing cables.

Battery powered vehicles offer the highest flexibility, however, they are typically heavier than the other options and require regular recharging. A research study by W. Jacobs found that LHDs required 1.5-2 tonnes of batteries which only allowed for 2-2.5 hours of working time with an estimated recharge time of 2 hours. This resulted in a vehicle availability of approximately 50%.[2]

Overhead power lines that enable trolley mechanisms are impractical for LHDs that require a high degree of manoeuverability. The use of tether trailing cables that are plugged into electrical infrastructure is typically the best option due to its ease of manoeuverability. eLHDs are ideal where hauling distances are short and operations are repetitive [3]

Advantages

eLHDs are becoming increasingly common due to the following advantages: [2]

- Zero emissions

- No exhaust gases results in better visibility and a better working environment [4]

Disadvantages

A major disadvantage of eLHDs is high capital costs compared to diesel vehicles. Cable control in trailing cable eLHDs is another issue. These eLHDs may lack the versatility to accomplish all required activities, especially at distance from the tether station. Additionally, there is the inherent danger posed by cables trailing the vehicles and potentially obstructing access by equipment. Extra care needs to be taken to avoid damaging cables.

The following disadvantages are of concern for eLHDs on trolley mechanisms:

Diesel vs. Electric LHDs

Table 2 gives an overview of the ventilation requirements for similar diesel and electric LHDs. It should be noted that the diesel equivalent LHD has many of the same payload and size specifications, and uses largely the same parts as the diesel LHD. [2]

Haul Trucks

Electric haul trucks are employed for ore transportation typically in difficult geological conditions, under stringent safety issues, and with large production requirements. Most electric haul truck designs have the following features: automatic trolley connection/disconnection, diesel motor/generator for off line duty, and a diagnostic system [7]. These trucks are designed in case they must disconnect from the line, the diesel engine starts automatically to ensure continuous function of the truck.

Advantages

Electric haul trucks are typically used due to the following advantages:

- Minimal demand on ventilation systems because they do not produce exhaust gases[8]

- No exhaust gases results in better visibility and a better working environment[4]

- They produce a smaller carbon footprint than standard diesel trucks

- Long asset life of approximately 60,000 hours

- Lower operating costs

- Lower cost per tonne

- Electric power leads to less demand on the mechanical systems of the trucks [9]

- This results in lower spare parts consumption and a longer life

- Can utilize steeper ramps which means shorter tunnels may be used

- Faster speeds going up steep ramps with shorter cycle times

The low operating costs are due to electricity being cheaper than diesel in most parts of the world [8]. In addition, low operating costs are due to the increase in efficiency by using electric motors. The electric haul trucks also require less maintenance as they fewer moving parts that could experience wear and tear. [8]

The major disadvantage of electric haul trucks is that they have high capital costs compared to diesel vehicles. This is because they are powered by an overhead trolley system that must be installed along the complete length of each haul road. Electric haul trucks are typically used in very deep mines because of the high ventilation costs associated with using diesel trucks, but they are not ideal for shallower operations. As a result, electric haul trucks are considered “necessity” equipment which mining companies will only choose to use if diesel trucks are not suitable.

Types of Trucks

A common electric haul truck manufacturer used in Canada is the Kiruna Truck Company. They have two alternating current (AC) models: The K635ED 35-tonne truck and the K1050ED 50-tonnes truck, both off which may be 2-wheel drive (2WD) and 4-wheel drive (4WD)[7]

The K635ED has a rear dump and side dump design when in 2WD that should only be used on road grades of 0-3%. When in 4WD, it has a rear dump design that may be used on road grades ranging from 0-20%. It has 480 kW power and can travel 18 km/h uphill loaded on a ramp of +15% grade, and can travel 21.6 km/h empty downhill. Figure 1 depicts this truck when not in operation.

The K1050ED also has a rear dump and side dump design when in 2WD that should only be used on road grades of 0-3%. When in 4WD, it has a rear dump design that may be used on road grades ranging from 0-18%. It has 800 kW power and can travel 19 km/h uphill loaded on a ramp of +15% grade, and can travel 21 km/h empty downhill. Figure 2 depicts this truck in operation in the Zinkgruvan Mine in Sweden [10] .

The Kiruna fleet of electric trucks is ideal due to the trucks’ ability to regenerate power back to the overhead electrical power trolley line when braking while travelling down the ramp. This is an additional energy efficient benefit [11]. Kiruna electric trucks are also twice as fast as diesel units on a 15% incline as there are fewer drivers and less complicated logistics [9]

Jumbo Drills

A jumbo drill is piece of mining equipment that tills into material to be mined. The drill holes are loaded with explosive material that is blasted, and the fragmented rock is sent out of the mine.

Function

An all-electric jumbo drill uses AC electric power, which is connected to a three phase induction motor mounted on the drill [12]. The motor drives a hydraulic circuit which moves hydraulic percussive rotary hammers on to the drilling face which develops the borehole for blasting. Electric jumbo drills can be used for both precutting and production blasting.
Upon completion of the drilling pattern at a face, the jumbo drill must move into the next stope of the mine. The drill is trammed from one location to another using an electric vehicle. The jumbo drill and tram both require connection to an electric power source.

Power Source

The electric jumbo drill is powered using a connection to an AC power source [12]. This connection has most commonly been from a power cord connected to a generator or large power source. Using a power cord in underground mines can be a major hazard from a health and safety perspective, as well as a possible cause of downtime in the event it is damaged. When a power cord is laying on the mine floor, it can be cut while moving or being run over by another piece of mobile equipment. If this cord is damaged or cut, it will require repairs. These repairs are a cause of downtime in a mine, and can add up to major production losses if required repairs are significant. Many mining companies hire specific cable runners or electricians whose sole purpose is to monitor, repair or replace these damaged cords in the event they are damaged or broken.

Drilling Innovation

A major machine provider, Sandvik, has recently released the first fully battery-trammed jumbo drill [13]. This drill does not require the use of any sort of power cords while being trammed, and batteries can be easily changed during the drilling cycle in order to ensure that the machine is constantly operable. In addition, the drill does not produce any emissions which is an important consideration for ventilation. The tram is also equipped with a laser scanner which provides a considerably more accurate drilling pattern when in operation. This can improve fragmentation in the drilling and blasting process and save valuable time in the drilling cycle.

Economics

Two areas where electric vehicles provide definite benefit are fuel/energy savings and ventilation savings.
As the world moves towards renewable energy and away from fossil fuels, it is expected that diesel prices will increase at a rate faster than electricity costs. Retail diesel cost (in real USD) have increased by approximately 20% in the last twenty years while retail industrial electricity costs have remained approximately the same.

Capital Costs

Electric LHDs have capital costs approximately 20% higher than traditional diesel [2]. Other sources argue additional costs such as a trailer with a diesel generator set could be required to move electric LHDs beyond the range of set power stations, adding an additional 10-20% to the purchase cost of an electric LHD [14]. An investigation into electric LHD capital cost premiums compared to diesel LHDs found that the premium becomes non-existent for larger bucket sizes. [6]

Operating Costs

There is conflict as to whether electric or diesel LHDs have higher operating costs. Operating costs are largely dependent on fuel/energy prices, differing due to varying assumed diesel and electricity prices making operating costs vary on a site-by-site basis. One perimeter pertaining to operating costs that is usually cheaper for electric equipment is maintenance. Although previously elaborated, electric equipment eliminates the need for high skilled diesel engine mechanics.

Average Annual Costs

An investigation into the average annual costs of electric and diesel vehicles found that diesel vehicles are slightly cheaper than electric vehicles. [12]

Economic Benefits

Savings in fuel and ventilation as well as other areas can be significant. Varaschin and De Souza found that electric vehicles can help realize total cash cost reductions of approximately 5%. [6] Figure 5 illustrates potential economic benefits of using electric equipment.

Case Study: Goldcorp’s Borden Mine

The Borden project is located near Chapleau, Ontario and made major headlines after Goldcorp announced it will be the first underground mine in the world which will use a fully “green fleet”. The entire fleet will consist solely of battery and electric power, and will eliminate all greenhouse gases (GHGs) associated with moving ore and waste rock. [15] This initiative is expected to reduce on-site CO¬2 emissions by approximately 50%, or 5,000 tons of GHGs per year. The company has partnered with leading equipment manufacturers, Sandvik Mining and MacLean Engineering, to develop battery and electricity operated machines such as drills, bolters, personnel carries and a haul truck.

The move is expected to significantly increase capital costs, however Brent Bergeron, Executive VP, stated that “by moving away from diesel… Goldcorp can avoid more than 7,500 tons of CO2 and eliminate 3 million litres of diesel fuel, 1 million litres of propane and 35,000 megawatt hours of electricity every year.” Based upon the life of the project, as well as the overall expected operational savings it will bring, the use of electric and battery operated machines can bring significant savings to the project.

Goldcorp is optimistic that by adopting the use of an all-electric site, significant benefits will be achieved at the Borden project. They are also hopeful that other companies in the industry will make the more environmentally-conscious move to integrate all-electric fleets moving forward. [16]

Challenges

There are several important challenges in the implementation of battery-electric vehicle fleets. The first is a lack of a single charging standard for battery-electric vehicles. Currently, there are a number of different manufacturers all doing different things in regards to charging infrastructure (batteries, chargers and electrical current requirements). This is a burden on the bottom line of a mining company as they are forced to order from only one manufacturer or duplicate infrastructure.

The second challenge relates to energy density. There are logistical issues engendered from the energy requirements and limitations of electric vehicles. Key areas where electric vehicles currently lack include the amount of work a vehicle can do on one charge and the length of recharging times. Glencore’s Onaping Depth project is implementing a significant electric fleet and reportedly plans to place over 100 battery chargers throughout the mine so that vehicles can take advantage of natural charging opportunities during breaks and shift changes. [17] The placement of charging infrastructure requires planning and takes up space that is often at a premium in underground mines. Another physical consideration is vehicle parking schemes, as those charging vehicles must not interfere with production.